Study of the influence of sand on rheological properties, bubble features and buildability of fresh foamed concrete for 3D printing

Abstract

Using sand to partially replace binder in the preparation of foamed concrete (FC) can reduce shrinkage, result in a lower carbon footprint, and enhance eco-friendliness. The hardening properties and application of 3D printed FCs (3DPFC) are closely related to its performance. The effects of sand content and fineness on the rheological properties, buildability, pressure field, and bubble features of the FC used for 3D printing were studied and discussed. It was found that the doped sand competed with water in the surrounding paste, thus increasing the interparticle interaction force and difficulty of bubble integration, resulting in the decrease of air content and bubble diameter of FC. The static yield stress and thixotropy of sand-containing FC depends on the thickness and rheological properties of the bubble-containing paste layer around the sand particles. Replacing the binder with sand, especially with fine sand, intensifies the pressure field in the FC during the mixing process. The buildability of 3DPFC is linearly correlated with the average bubble diameter of FC. A formula is proposed to predict the buildability of 3DPFC based on the static yield stress and air content.